1. Field of the Invention
The present invention relates to a chain wheel mounting structure in fork lifts and, more particularly, relates to a chain wheel mounting structure improving a front visual field from the driver's seat.
2. Description of the Prior Art
In a conventional fork lift, a two-side supported structure as shown in FIG. 4 or a cantilever structure as shown in FIG. 5 has conventionally been used as the chain wheel mounting structure. In the two-side supported structure of FIG. 4, two pairs of wheel brackets 24a are welded to the lower surface of a chain beam 23 which connects piston rods 22 of left and right lift cylinders 21 to each other, and a support pin 25a for rotatably supporting a chain wheel 26 is fitted horizontally into each pair of wheel brackets 24a in a manner capable of being pulled out therefrom. Such a two-side supported structure is disclosed for example in Japanese Utility Model Laid-Open Application No. 2-64590.
Further, in the cantilever structure shown in FIG. 5, a wheel bracket 24b having a support pin 25b fixed thereto by means of welding or integrally formed thereon is welded to the lower surface of a chain beam 23 which connects piston rods 22 of left and right lift cylinders 21 to each other. A chain wheel 26 is then mounted in a manner rotatable with respect to the support pin 25b. Such a cantilever structure is disclosed for example in Japanese Patent Laid-Open Application No. 62-255395.
In the case of the two-side supported structure, however, a distance L1 from the lift cylinder 21 to the center of a lift chain 27 is larger due to the fact that two wheel brackets 24a are provided in each pair, whereby a chain pitch L2 between the left and right lift chains 27 becomes smaller.
Further, in the case of cantilever structure shown in FIG. 5, the distance L1 from the cylinder 21 to the center of the lift chain 27 must be provided large enough to make possible attachment/detachment of the chain wheel 26 with respect to the support pin 25b. As a result, the chain pitch L2 between the left and right lift chains 27 becomes smaller.
Specifically, in a fork lift of the free lift or semi-free lift having an extent of freedom L for lifting/lowering a load without raising the total height of the mast, there is a restriction that the wheel bracket 24a, 24b must be provided on the lower surface of the chain beam 23. For this reason, in the cases of both two-side supported structure and one-side supported structure as described, the lift chain 27 is present at an inner position distant from the lift cylinder 21 as a member obstructing the visual field. There is thus a problem that the front visual field is narrower comparing to a standard type fork lift in which the lift chain may be positioned relatively close to the lift cylinder by providing a wheel bracket having a support pin facing inward, on the back surface of an inner mast.
It should be noted that, when easiness of pulling out the support pin 25a is considered in the case of the above-described two-side supported structure, loose fitting is required between the support pin 25a formed of a parallel pin and the pin hole on the wheel bracket 24b into which the support pin 25a is inserted. Accordingly, if such loose fit is applied to the one-side supporting structure, the support pin 25a sloped with respect to the pin hole is brought into partial contact with the pin hole, and the stress is concentrated to that portion where breaking may occur. Thus, the one-side supported structure based on fitting method has not been employed for the reason of strength as described.
In view of the above problems, it is an object of the present invention to provide a chain wheel mounting structure of fork lift which is effective in improving the front visual field.